Method for coating metallic surfaces and use of the substrates coated in this manner

ABSTRACT

The invention relates to a method for coating metallic surfaces by a manganese-zinc phosphatizing process, using an aqueous phosphatizing solution, in which nickel is deliberately not added. Said method is characterized in that the zinc:manganese weight ratio of the phosphatizing solution is maintained in the region of between 0.05:1 and 0.99:1 and that the phosphatizing solution has the following contents: between 0.05 and 5 g/l zinc, between 0.075 and 5.2 g/l manganese and between 0.008 and 0.050 g/l copper and/or hexafluoride complexes of titanium, hafnium and/or zirconium totalling between 0.002 and 0.5 g/l, calculated as F 6 . The invention also relates to the use of the metal parts coated in this manner.

[0001] The present invention relates to a process for coating metallicsurfaces as well as the use of the substrates with metallic surfacescoated by the process according to the invention. This process isintended to serve as a pretreatment before a further coating, inparticular paint application, or as a treatment without subsequentcoating.

[0002] In zinc phosphating on galvanised substrates and in thesubsequent painting, in particular with cathodic dipping paint, paintadhesion problems always arise, in which small or even relatively largeparts of the overall paint structure may become detached and the paintcan be removed without any difficulty. In a cross-hatch adhesion testtotal detachment can be detected in a part of the test body. In thisconnection the detachment normally occurs between the galvanised surfaceand the phosphate layer with the paint structure.

[0003] In the past these problems were circumvented on an industrialscale by adding nickel to the phosphating solution in an amount suchthat this generally had nickel contents in the range from 05 to 1.5 g/l.

[0004] In zinc-manganese-nickel phosphating generally zinc contents werechosen in the range from 0.6 to 2 g/l and manganese contents were chosenin the range from 0.4 to 1 g/l, the zinc content normally being higherthan the manganese content.

[0005] On account of the toxicity and environmental incompatibility,increased nickel contents in the phosphating solution, which lead tounavoidable high heavy metal contents in the waste water, in thephosphate slurry and in the grinding dust, are becoming increasinglyless acceptable. Some attempts have therefore been made to operate withnickel-free or at least low nickel content phosphating solutions. Thesephosphating solutions have up to now still not been widely adoptedhowever, and in addition have hitherto also continued to exhibitsignificant disadvantages compared to the high nickel contentphosphating processes. When hitherto phosphating was carried out withlow nickel contents in the automobile industry, problems arose onaccount of variable paint adhesion, with the result that these trialswere not continued further.

[0006] Prephosphating has hitherto been used for galvanised steel stripmaterial. Prephosphating is nowadays normally understood to denote aphosphating process in which metallic substrates are phosphated eitherwithout prior cleaning directly after the galvanising or are phosphatedfollowing a prior cleaning if no galvanising or a storage of optionallyoiled substrates is chosen, and are then phosphated once more. Cuttingand/or working of the substrates, forming, bonding to other parts thathave optionally also been prephosphated, and/or welding of thesubstrates may take place between the prephosphating and the secondphosphating (=post-phosphating). However, according to the applicant'sknowledge up to now no prephosphating processes are known that can becarried out largely or completely free of nickel without significantloss of quality.

[0007] DE-A1-40 13 483 describes a process for the phosphating of metalsurfaces with aqueous, acidic phosphating solutions that contain zinc,manganese, copper, phosphate and oxidising agents as well as only tracesof nickel, in which the concentration of Fe²⁺ ions should be kept below0.1 g/l. Copper contents in the range from 3 to 5 mg/l are mentioned inthe examples. Serious problems may however arise with the phosphatingsolutions mentioned there on galvanised surfaces, while the quality ofthe tri-cation processes based on high nickel content Zn—Mn—Niphosphating is achieved.

[0008] DE-A1-42 10 513 relates to a process for producingcopper-containing, nickel-free phosphate layers by spraying and/ordipping with a phosphating solution that contains 0.2 to 2 g/l of zinc,5 to 30 g/l of P₂O₅, 0.005 to 0.025 g/l of copper and 0.5 to 5 g/l of acompound based on hydroxylamine, calculated as HA, by means of whichphosphate crystals are produced having an edge length in the range from0.5 to 10 μm. Low pore content, compact phosphate layers with a lowsurface density, excellent corrosion resistance and very good paintadhesion are said to be produced in this way. All copper-containingembodiments either have a Zn:Mn ratio of >1 or a high nickel content.

[0009] EP-A-0 675 972 describes a process for the production ofcopper-containing, largely nickel-free zinc phosphate layers with anaqueous composition, as well as the aqueous composition itself, whichcontains 0.026 to 0.074 g/l of copper, 0.45 to 2 g/l of zinc, 0.1 to 10g/l of compounds based on hydroxylamine, calculated as HA, total acidvalues in the range from 5 to 40 points as well as free acid in therange from −0.5 to +0.8 point, and which may preferably contain totalcontents of up to 2 g/l of manganese and cobalt. This process is said tobe more environmentally friendly and cheaper than the conventionalnickel-containing phosphating processes, and coatings of the samequality as those produced by conventional ZnMnNi phosphating are said tobe obtained. All copper-containing embodiments either have a Zn:Mn ratioof >1 or even no manganese at all.

[0010] DE-A1-196 06 017 describes a process for the phosphating of metalsurfaces with aqueous, acid phosphating solutions that contain specificcontents of zinc but only traces of manganese and copper in addition tophosphate and at least one accelerator and also, as far as possible,only traces of nickel. No aqueous compositions with a Zn:Mn ratio of <1can be employed in this process.

[0011] DE-A1-196 34 685 discloses an aqueous solution for producingphosphate layers as well as the associated phosphating process, in whichthe phosphating solution is adjusted with zinc, phosphate,nitroguanidine as accelerator and with further additives so thatphosphate crystals with a maximum edge length of <15 μm are produced atcomparatively low temperatures, and a low layer weight and a good paintadhesion are achieved. All copper-containing embodiments have a Zn:Mnratio of >1, or with a Zn:Mn ratio of <1 have copper contents of only upto 0.005 g/l. The use of nitroguanidine as accelerator is however oftendisadvantageous, since with prolonged use of the phosphating bath—insome cases even after a day—in the presence of copper a bath poison isformed that seriously affects the layer formation on steel surfaces. Ifnecessary the bath then has to be discarded and reconstituted.

[0012] In the manganese-zinc phosphating processes commonly used at thepresent time contents of zinc to manganese in the ratio of about 1.3:1to 3:1 are normally used. It has now surprisingly been found that thepaint adhesion was significantly improved if the weight ratio of zinc tomanganese is less than 1:1.

[0013] The object of the invention is therefore to obviate thedisadvantages of the prior art in a phosphating system free of addednickel and also to eliminate the serious paint adhesion problems, inparticular on galvanised or zinc surfaces. In particular a processshould be provided for coating galvanised surfaces that is as far aspossible industrially suitable for coating individual parts as well asfor coating strip material at high speeds. The phosphating processshould be at least equivalent as regards corrosion resistance to thephosphating systems that are currently used for pretreatment ortreatment, but should also be inexpensive and should be able to be usedin an environmentally friendly manner, in particular largely free ofnickel. The object consisted in particular of providing an industriallyusable, largely nickel-free phosphating process for prephosphating.

[0014] This object is achieved by a process for the coating of metallicsurfaces by manganese-zinc phosphating with an aqueous phosphatingsolution, in which no nickel is intentionally added to the phosphatingsolution, which process is characterised in that

[0015] the zinc:manganese weight ratio of the phosphating solution ismaintained in the range from 0.05:1 to 0.99:1,

[0016] and that the phosphating solution has the following contents:

[0017] zinc in the range from 0.05 to 5 g/l, manganese in the range from0.075 to 5.2 g/l, as well as copper in the range from 0.008 to 0.050 g/land/or

[0018] a total amount of 0.002 to 0.5 g/l of hexafluoride complexes ofboron, aluminium, titanium, hafnium and/or zirconium, calculated as F₆.

[0019] It was surprisingly found that with phosphating solutions free ofadded nickel significantly better coating results can be achieved with aZn:Mn ratio of less than 1:1 without the occurrence of the otherwisedescribed problems of defective paint adhesion. The zinc:manganeseweight ratio of the phosphating solution is preferably in the range from0.5:1 to 0.9:1, in particular in the range from 0.65:1 to 0.8:1.Surprisingly the coating is of high quality over a very wide range ofthe zinc:manganese weight ratios of the phosphating solution. If howeverin very acidic solutions the zinc content drops below 0.2 g/l, thecoating quality on high iron content surfaces may also fall.

[0020] The phosphating solution preferably has zinc contents in therange from 0.5 to 3.8 g/l, for strip material especially in the rangefrom 1.6 to 3.5 g/l and for parts especially in the range from 0.6 to 2g/l and particularly preferably in the range from 0.8 to 1.1 g/l. In thecase of phosphating by spraying of parts a zinc content in the rangefrom 0.3 to 1.3 g/l is often sufficient, whereas with dipping, zinccontents in the range from 0.7 to 1.9 g/l are necessary. For theprephosphating the zinc content is preferably in the range from 1.1 to3.5 g/l. If the zinc content of the phosphating solution is too low,then the layer formation is incomplete, in particular on high ironcontent surfaces. With zinc contents of less than 0.4 g/l, in certaincircumstances good coating results can no longer be expected in the caseof parts, in particular on high iron content surfaces. With zinccontents greater than 2.5 g/l the paint adhesion may already deteriorateslightly, even if the manganese contents are only in the range fromabout 2.55 to 2.8 g/l. The smaller the zinc:manganese weight ratio, themore efficiently is this effect controlled, so that with zinc contentsof greater than 3.5 g/l the paint adhesion may deteriorate slightly onlywith manganese contents in the range from about 3.55 to 3.8 g/l.

[0021] The term “zinc surfaces” within the context of the presentinvention includes not only the surfaces of zinc alloys, but alsogalvanised surfaces, in particular those of iron alloys and steel.Similarly, the terms “aluminium surfaces” include surfaces of aluminiumand aluminium alloys, and “iron surfaces” include surfaces of high ironcontent alloys.

[0022] The manganese content of the phosphating solution is preferablyin the range from 0.2 to 4 g/l, for strip material especially in therange from 1.7 to 3.0 g/l, and for parts in particular in the range from0.5 to 3.8 g/l and particularly preferably in the range from 1 to 3 g/l.A significant improvement in the paint adhesion on the phosphatedsurfaces is achieved by an increased manganese content. For theprephosphating the manganese content is preferably in the range from 1.9to 2.4 g/l.

[0023] The copper content is preferably in the range from 0.009 to 0.045g/l, particularly preferably in the range from 0.010 to 0.040 g/l, andfor strip material especially in the range from 0.012 to 0.25 g/l andfor parts especially in the range from 0.012 to 0.030 g/l. For theprephosphating the copper content is preferably in the range from 0.008to 0.048 g/l, particularly preferably in the range from 0.017 to 0.043g/l. In the prephosphating experiments it was found that the results asregards corrosion protection and paint adhesion in the BMW paintstructure improved continuously, starting from the poor results withcopper-free phosphating solutions to the good results starting from0.017 g/l of copper; it was also found however that these results maybecome worse again above about 0.040 to 0.043 g/l of copper.

[0024] In the resultant phosphate coating the copper content wasgenerally found to be in the range from 5 to 35 mg/m². By adding minoramounts of copper better coating results and paint adhesion values canbe obtained than without adding copper and also with very smalladditions of copper. In particular the corrosion resistance of an ironsurface is improved by adding copper. Copper contents in the range from0.020 to 0.050 g/l do not lead to poorer quality layers; however, highercopper contents in combination with too long a residence time of thesubstrates in the baths can result in a non-uniform deposition of copperon the surfaces to be phosphated.

[0025] The paint adhesion can be significantly improved by the additionof small amounts of titanium, hafnium and/or zirconium hexafluoride.These amounts are preferably in the range from 0.003 to 0.3 g/l,particularly preferably in the range from 0.004 to 0.1 g/l. However, inthe case of aluminium surfaces these hexafluorides should generally belimited to values of up to 0.05 g/l—calculated as F₆—since otherwisethere may be a marked interference in the layer formation. In addition acontent of silicon hexafluoride, in particular in the range from 0.5 to4 g/l SiF₆ and preferably in the range from 1 to 3 g/l, may beadvantageous in order to improve the homogeneity of the phosphate layer,in particular with zinc surfaces, and to stabilise the bath as regardszinc precipitation in the presence of free fluoride and thereby toensure that the zinc contents remain dissolved in the bath.

[0026] Preferably the phosphating solution is free of additions of oxoanions of halogens, in particular of nickel, and of aluminium contentsgreater than 0.05 g/l. Even if no nickel is intentionally added to thephosphating solution, on account of the nickel content of the metallicsurface of the substrate to be coated, on account of the possiblynickel-containing vessel materials and to a minor extent on account oftrace impurities in the additives, the bath may have a nickel content ofup to 0.1 g/l and in extreme cases, on account of very high nickelcontent metallic surfaces, even up to 0.25 g/l.

[0027] Whereas in the frequently employed nickel-containing phosphatingin many cases 1 to 2 g/l of nickel are used in the phosphating, in thecase of the copper-containing and largely or wholly nickel-freephosphating according to the invention it is possible to manage withonly 0.008 to 0.050 g/l of copper. Whereas with the aforementionednickel contents in the bath about 10 to 20 mg/m² of nickel and 0.7 to1.3 wt. % of nickel are contained in the phosphate coating, despite themuch lower copper contents in the phosphating solution about 5 to 35mg/m of copper and 0.3 to 2 wt. % of copper are found in the phosphatecoating according to the invention.

[0028] The coating process according to the invention may bedistinguished by the fact that the phosphating solution has a content ofsilver in the range from 0.0001 to 0.05 g/l, preferably in the rangefrom 0.001 to 0.03 g/l.

[0029] In addition the phosphating solution may also contain contents ofFe²⁺ ions in the range of up to about 1 g/l, especially in the case ofiron surfaces. Neither minor nor larger Fe²⁺ contents in the phosphatingbath normally interfere in widely different metal surfaces.

[0030] In the coating process according to the invention the phosphatingsolution may have a content of sodium in the range from 0.01 to 10 g/land/or a content of potassium in the range from 0.01 to 10 g/l,preferably a content of sodium in the range from 1 to 5 g/l, mostparticularly preferably in the range from 3 to 4 g/l. The addition ofsodium is usually advantageous in order to reduce the levels of freeacid. Furthermore the addition of sodium may help to precipitate, forexample as cryolite, a part of the aluminium content in the phosphatingsolution, which depending on the circumstances can adversely affect thelayer formation on steel and in some cases also the paint adhesion.Potassium is less recommended than sodium, not only on account of thesomewhat higher costs but also, in certain circumstances, on account ofthe poorer coat properties.

[0031] In the coating process according to the invention thezinc:phosphate weight ratio of the phosphating solution may bemaintained in the range from 0.016:1 to 1.33:1, phosphate beingcalculated as PO₄. Preferably this ratio is maintained in the range from0.02:1 to 0.8:1, particularly preferably in the range from 0.025:1 to0.25:1.

[0032] In the coating process according to the invention the phosphatingsolution may have a content of phosphate in the range from 3 to 75 g/l,phosphate being calculated as PO₄, preferably in the range from 7.5 to37 g/l, particularly preferably in the range from 10 to 30 g/l, mostparticularly preferably in the range from 12 to 26 g/l, and in the caseof strip material especially in the range from 17 to 21 g/l. For theprephosphating the phosphate content is preferably in the range from 12to 18 g/l. If the weight ratio (zinc+manganese):phosphate is too high,then the bath may tend to become unstable unless the content of freeacid is increased, failing which there may be a fairly markedprecipitation of phosphate. If this weight ratio is too low, then thecorrosion resistance and the paint adhesion may be impaired.

[0033] In the coating process according to the invention the phosphatingsolution may have a chloride content in the range from 0.01 to 10 g/land/or a chlorate content in the range from 0.01 to 5 g/l, preferably achloride content in the range from 0.1 to 6 g/l and preferably achlorate content in the range from 0.1 to 3 g/l. An addition of chlorideand possibly also chlorate or chlorate alone in specific amounts shouldbe avoided in the phosphating of zinc surfaces on account of the dangerof the formation of white spots (specks), if nitrate and/or nitrite arepresent.

[0034] Since aluminium contents from aluminium or aluminium-zincsurfaces may be a problem without the presence of fluoride, it isaccordingly advantageous to add free fluoride, for example as HF or assodium bifluoride, and/or silicon hexafluoride. Silicon hexafluoride canstabilise the phosphating solution, i.e. reduce the precipitation ofphosphates, and can also reduce the formation of specks in zincsurfaces.

[0035] In the coating process according to the invention the phosphatingsolution may have a content of free fluoride in the range from 0.001 to0.8 g/l, preferably in the range from 0.01 to 0.5 g/l, particularlypreferably in the range from 0.03 to 0.2 g/l, calculated as F. A contentof free fluoride may be beneficial for the phosphating of aluminiumsurfaces and for the precipitation of aluminium. Typically about 1 to60% of the total fluorine content is present in the form of freefluoride and the remainder is present as complex fluoride and asunassociated hydrofluoric acid.

[0036] In the coating process according to the invention the phosphatingsolution may have a content of total fluoride in the range from 0.01 to5 g/l, preferably in the range from 0.1 to 1 g/l, calculated as F.

[0037] In the coating process according to the invention the phosphatingsolution may have a content of at least one accelerator in the rangefrom 0 to 40 g/l, preferably in the range from 0.02 to 30 g/l,particularly preferably in the range from 0.1 to 20 g/l. The acceleratormay help to suppress the formation of hydrogen bubbles on the surfaces.Due to the better contact with the surface to be coated—since this isnot partially covered by hydrogen bubbles—more crystal nuclei can beformed there. The presence of an accelerator is not absolutelyessential, especially in the case of zinc surfaces. An accelerator ishowever of considerable advantage, generally in the case of aluminium,iron and steel surfaces, since in this way the phosphate layer can beproduced in a finely crystalline form because the phosphate layer canthereby be sealed more quickly and easily and because the corrosionprotection and the paint adhesion can be improved in this way.

[0038] In the coating process according to the invention the phosphatingsolution may have a nitrite content in the range from 0.01 to 0.3 g/l, anitrate content in the range from 1 to 30 g/l, a content of compoundsbased on peroxide in the range from 0.001 to 3 g/l, preferably in therange from 0.01 to 0.15 g/l, calculated as H₂O₂, a content ofnitrobenzenesulfonate (NBS), nitropropane, nitroethane and/or othernitro-organic compounds with oxidising properties—with the exception ofcompounds based on nitroguanidine—with a total content in the range from0.1 to 3 g/l calculated as NO₂, a content of compounds based onnitroguanidine in the range from 0.1 to 5 g/l, a chlorate contentpreferably in the range from 0.05 to 4 g/l, a content of reducing sugarcompounds in the range from 0.1 to 10 g/l and/or a content of compoundsbased on hydroxylamine (HA) in the range from 0.1 to 6 g/l, calculatedas HA. Chlorate additions are normally used in nitrite-free andnitrate-free baths if zinc surfaces are to be coated. For theprephosphating the nitrate content is preferably in the range from 12 to19 g/l. If low nitrate contents or even nitrate-free solutions are usedin the prephosphating, then an addition of 0.5 to 3 g/l of peroxide,calculated as H₂O₂, is preferred.

[0039] Preferably the phosphating solution has a content of nitrite inthe range from 0.05 to 0.2 g/l. Although nitrite, like thenitrogen-containing gases that may possibly be formed therefrom, has thedisadvantage that it is extremely toxic, nitrite has the advantage thatit is inexpensive and its action is very well known and can beeffectively controlled. Preferably the phosphating solution has acontent of nitrate in the range from 5 to 25 g/l. On account of the weakaction of this accelerator higher contents of nitrate are oftenemployed. Preferably the phosphating solution has a content of compoundsbased on peroxide in the range from 0.01 to 0.1 g/l. Preferably thephosphating solution has a total content of nitrobenzenesulfonate and/orother nitro-organic compounds with oxidising properties in the rangefrom 0.5 to 2 g/l. Preferably the phosphating solution has a content ofcompounds based on hydroxylamine in the range from 0.5 to 2 g/l.Preferably the ratio of the contents of compounds based onhydroxylamine, calculated as HA, to the sum total of zinc and manganesein the phosphating solution is in the range from 1:2 to 1:4. However, incertain circumstances hydroxylamine may be catalytically decomposed inthe presence of a specific copper content.

[0040] At least one compound based on perboric acid, lactic acid,tartaric acid, citric acid and/or a chemically related hydroxycarboxylicacid may advantageously be added in order to stabilise the bath, theconcentrate or the replenishment solution, in particular to prevent orreduce precipitations from one of these solutions, as well as toincrease the crystallinity of the phosphate layer, whereby the waterresistance of the phosphate layer is substantially improved.

[0041] Furthermore, an addition of a polymeric alcohol may also beadvantageous in order to form phosphoric acid esters with this alcohol,especially during the drying, which have a beneficial effect aslubricants in forming. At the same time the addition of a polymericalcohol may affect the reaction with the excess free phosphoric acidthat is possibly present in the phosphating solution, by improving thecrystallinity and the water resistance of the phosphate coating.

[0042] It was surprisingly found that the prephosphating usingcopper-containing phosphating solutions with a Zn:Mn weight ratio ofless than 1:1 leads to extremely good paint adhesion results, inparticular on galvanised surfaces, if post-phosphating was carried outwholly or largely nickel-free after the prephosphating and before thepainting. It was also surprisingly found that, due to the almostcomplete absence of nickel, the good results of a nickel-containingprephosphating layer as regards corrosion protection, formability,bondability and weldability are retained, and in the case of formabilityhowever lead to even better results. The prephosphating is particularlysuitable for the implementation of a rinse phosphating by sprayingand/or dipping with spraying/dipping times approximately in the rangefrom 3 to 15 seconds and at a temperature in the range from 45° to 65°C., particularly with galvanised surfaces.

[0043] The prephosphating is particularly suitable for the production ofstrip material by rinse processes, in which rinsing is performed afterthe application of the phosphate layer. This process is suitable inparticular for automobile production.

[0044] In the coating process according to the invention the phosphatingsolution for the prephosphating may contain the following amounts:

[0045] zinc in the range from 0.4 to 5 g/l,

[0046] manganese in the range from 0.5 to 5.2 g/l,

[0047] copper in the range from 0.008 to 0.050 g/l.

[0048] If prephosphating, in particular prephosphating according to theinvention, is carried out, then post-phosphating according to theinvention may also be carried out in the following way, in which firstof all prephosphated, optionally at least partially formed/shaped andoptionally at least partially welded metallic substrates are phosphatedby manganese/zinc phosphating with an aqueous phosphating solution inwhich no nickel is intentionally added to the phosphating solution orthe phosphating solution only has a nickel content of up to 0.3 g/l,which is characterised in that

[0049] the phosphating solution contains the following amounts:

[0050] zinc in the range from 0.05 to 5 g/l and manganese in the rangefrom 0.075 to 5.2 g/l.

[0051] The coating results and corrosion protection results that wereobtained are outstanding, especially with zinc-containing surfaces.

[0052] In the coating process according to the invention the phosphatingsolution may have the following contents, in particular for parts:

[0053] zinc in the range from 0.6 to 1.4 g/l,

[0054] manganese in the range from 0.7 to 2.0 g/l, zinc:manganese weightratio in the range from 0.6:1 to 0.95:1,

[0055] phosphate calculated as PO₄ in the range from 12 to 25 g/l,

[0056] zinc:phosphate weight ratio in the range from 0.02 to 0.12,

[0057] copper in the range from 0.008 to 0.025 g/l,

[0058] total content of fluoride as free fluoride, as bound fluorideand/or as at least one complex fluoride, in the range from 0 to 6 g/l,calculated as F,

[0059] wherein the complex fluoride SiF₆ is contained in an amount inthe range from 0 to 4.5 g/l calculated as SiF₆, and

[0060] nitrate in the range from 0 up to 22 g/l and/or at least oneother accelerator selected from the group comprising nitrite orcompounds based on hydroxylamine, nitroguanidine and/or peroxide, ineach case in the range from 0.01 to 2 g/l.

[0061] In the coating process according to the invention the phosphatingsolution may have the following contents, in particular for stripmaterial, particularly preferably for galvanised strip surfaces:

[0062] zinc in the range from 0.1 to 4 g/l,

[0063] manganese in the range from 0.5 to 5 g/l,

[0064] zinc:manganese weight ratio in the range from 0.02:1 to 0.9:1,

[0065] phosphate calculated as PO₄ in the range from 10 to 40 g/l,

[0066] zinc:phosphate weight ratio in the range from 0.0025 to 0.4,

[0067] copper in the range from 0.008 to 0.032 g/l,

[0068] total content of fluoride as free fluoride, as bound fluorideand/or as at least one complex fluoride in the range from 0 to 6 g/l,calculated as F,

[0069] wherein the complex fluoride SiF₆ is contained in an amount inthe range from 0 to 4.5 g/l, calculated as SiF₆, and

[0070] nitrate in the range from 0 up to 22 g/l and/or at least onefurther accelerator selected from the group comprising nitrite orcompounds based on hydroxylamine, nitroguanidine and/or peroxide, ineach case in the range from 0.01 to 2 g/l.

[0071] In the coating process according to the invention the phosphatingsolution for the prephosphating may preferably have the followingcontents:

[0072] zinc in the range from 1.3 to 2.3 g/l,

[0073] manganese in the range from 1.7 to 2.6 g/l,

[0074] zinc:manganese weight ratio in the range from 0.5:1 to 0.95:1,

[0075] phosphate calculated as PO₄ in the range from 10 to 20 g/l,

[0076] zinc:phosphate weight ratio in the range from 0.06 to 0.23,

[0077] copper in the range from 0.008 to 0.048 g/l,

[0078] total content of fluoride as free fluoride, as bound fluorideand/or as at least one complex fluoride in the range from 0 to 6 g/l,calculated as F,

[0079] wherein the complex fluoride SiF₆ is contained in an amount inthe range from 0 to 4.5 g/l, calculated as SiF₆, and

[0080] nitrate in the range from 0 up to 30 g/l and/or at least onefurther accelerator selected from the group comprising nitrite orcompounds based on hydroxylamine and/or nitroguanidine, in each case inthe range from 0.01 to 2 g/l, or peroxide in the range from 0.01 to 3g/l.

[0081] In this connection the nitrate content, if nitrate is added asaccelerator, is preferably in the range from 3 to 22 g/l, and thecontent of at least one compound based on peroxide is in the range from0.5 to 2.5 g/l, especially if a nitrate-free process is used.

[0082] In the coating process according to the invention the phosphatingsolution may also preferably have the following contents:

[0083] zinc in the range from 0.6 to 1.4 g/l,

[0084] manganese in the range from 0.7 to 2.0 g/l,

[0085] zinc:manganese weight ratio in the range from 0.6:1 to 0.95:1,

[0086] phosphate calculated as PO₄ in the range from 12 to 25 g/l,

[0087] zinc:phosphate weight ratio in the range from 0.02 to 0.12,

[0088] total content of fluoride as free fluoride, as bound fluorideand/or as at least one complex fluoride in the range from 0.012 to 6 g/lcalculated as F,

[0089] wherein the total content of complex fluorides of titanium,hafnium and/or zirconium is in the range from 0.002 to 0.5 g/l,calculated as F₆, and wherein the complex fluoride SiF₆ is contained inan amount in the range from 0 to 4.5 g/l, calculated as SiF₆, and

[0090] nitrate in the range from 0 up to 22 g/l and/or at least onefurther accelerator selected from the group comprising nitrite orcompounds based on hydroxylamine, nitroguanidine and/or peroxide, ineach case in the range from 0.01 to 2 g/l.

[0091] In the coating process according to the invention the metallicsubstrates may be coated for a time of up to 20 minutes, strip materialpreferably being coated for a time ranging from 0.1 to 120 seconds andparticularly preferably for a time ranging from 0.3 to 60 seconds, andparts preferably being coated for a time ranging from 1 to 12 minutesand particularly preferably for a time ranging from 2 to 8 minutes.

[0092] In the coating process according to the invention the temperatureof the phosphating solution for the coating may be in the range from 10°to 72° C., for strip material preferably in the range from 40° to 70° C.and for parts preferably in the range from 20° to 60° C. andparticularly preferably in the range from 32° to 58° C.

[0093] In the coating process according to the invention the free acidlevel may be from 0.1 to 10 points, the total acid may be from 5 to 50points, the total acid according to Fischer may be from 3 to 25 points,and the ratio of the free acid to total acid according to Fischer (Svalue) may in particular be in the range from 0.01 to 0.7, wherein theconcentration of free acid is preferably 0.15 to 4 points, theconcentration of total acid according to Fischer is preferably 12 to 35points and the ratio of the free acid to total acid according to Fischer(S value) is preferably in the range from 0.03 to 0.3. For theprephosphating it is particularly preferred to have values of the freeacid in the range from 3 to 4.4 points and values of the total acidaccording to Fischer in the range from 18.5 to 21 points and thus an Svalue in the range from 0.14 to 0.24.

[0094] In order to determine the free acid 1 ml of the phosphatingsolution, after dilution to ca. 50 ml with distilled water andoptionally with the addition of K₃(Co(CN)₆) or of K₄(Fe(CN)₈) in orderto remove interfering metal cations, is titrated with 0.1 M NaOH usingdimethyl yellow as indicator until the colour turns from pink to yellow.The amount of 0.1 M NaOH used in ml represents the value of the freeacid (FA) in points.

[0095] The total content of phosphate ions is determined following themeasurement of the free acid, by titrating the titration solution afteraddition of 20 ml of 30% neutral potassium oxalate solution, with 0.1 MNaOH using phenolphthalein as indicator until the colour turns fromcolourless to red. The consumption of 0.1 M NaOH in ml between thecolour change with dimethyl yellow and the colour change withphenolphthalein corresponds to the total acid according to Fischer(TAF). If this value is multiplied by 0.71, the total content ofphosphate ions is obtained (see W. Rausch: “Die Phosphatierung vonMetallen”, Eugen G. Leuze-Verlag 1988, pp. 300 ff).

[0096] The so-called S value is obtained by dividing the value of thefree acid by the value of the total acid according to Fischer.

[0097] The total acid (TA) is the sum total of the contained divalentcations as well as free and bound phosphoric acids (the latter beingphosphates). The total acid is determined from the consumption of 0.1 Msodium hydroxide using phenolphthalein as indicator. This consumption inml corresponds to the point value of the total acid.

[0098] In the coating process according to the invention the pH of thephosphating solution may be in the range from 1 to 4, preferably in therange from 2.2 to 3.6.

[0099] In the coating process according to the invention the phosphatingsolution may be applied to the surface of the substrates by knifecoating, flow coating, spraying, sprinkling, brushing, dipping,nebulising or rolling, individual process steps being able to becombined with one another—in particular spraying and dipping, sprayingand squeezing off as well as dipping and squeezing off, and optionallysubsequent squeezing off.

[0100] In the coating process according to the invention substrates witha metallic surface predominantly containing aluminium, iron, copper,magnesium, tin or zinc, in particular surfaces of at least one of thematerials based on aluminium, iron, steel, zinc and/or alloys with acontent of aluminium, iron, copper, magnesium, tin or zinc, can becoated with the phosphating solution.

[0101] In the coating process according to the invention a phosphatecoat can be precipitated from the phosphating solution that has a layerweight in the range from 0.2 to 6 g/m², preferably in the range from 1to 4 g/m². Particularly in the case of aluminium surfaces it may bedesirable in some cases to apply only very low layer weights. In thepretreatment or treatment of surfaces of aluminium or aluminium alloysit is not absolutely essential to achieve a high degree of covering inthe phosphating process. A layer weight of the phosphate layer in therange from 0.2 g/m² to 1 g/m² is sufficient. A layer weight of up to 6g/m² and thus a complete covering is however not disadvantageous, apartfrom an increased consumption of chemicals. With surfaces of iron, steeland zinc an almost complete or complete covering with the phosphatelayer is however necessary. This is achieved with a layer weight in therange from 1 g/m² to 6 g/m². In the prephosphating a layer weight in therange from 0.8 to 2.4 g/m² is particularly preferred, especially 1 to 2g/m², in particular if the substrates with the prephosphate coating areto be used for welding.

[0102] In the coating process according to the invention metallicsurfaces may be cleaned, pickled, rinsed and/or activated before thephosphating. The cleaning is preferably carried out with an alkalineagent and takes place in particular over a time ranging from 10 secondsto 15 minutes. A weak alkaline cleaning agent may be employed formetallic surfaces, in most cases over 2 to 4 minutes. The treatmenttimes are correspondingly shorter for strong alkaline cleaning agents.It may be advantageous to add a titanium-containing activator to thecleaning agent. An acidic cleaning may also be chosen in particular foraluminium and aluminium alloys.

[0103] In principle any water of sufficiently pure quality is suitablefor the subsequent rinsing. Tap water is recommended. If the activationcan take place in a separate bath or rinsing step, which is mostadvantageous, then fully deionised water should be used as solvent afterprior rinsing. An activation is often very advantageous in order to formcrystal seeds. The activation may in particular be based on titanium. Anactivation over 10 to 30 seconds is often sufficient, although inprinciple the activation time may range from 0.1 second up to at least 5minutes. The activation may also be longer than 5 minutes, though thisdoes not have any beneficial effect. It may be advantageous to addcopper and/or one of the additives known in principle to the activation.

[0104] In the coating process according to the invention the phosphatedsubstrates may be rinsed at least once and optionally treated after arinse procedure or between two rinse procedures, with a post-rinsesolution to confer additional passivation. In principle any water ofsufficiently pure quality is suitable for the rinsing after thephosphating. Tap water or fully deionised water is recommended—forexample dipping in cold tap water for 10 seconds—followed in the nextrinse step by fully deionised water—for example spraying with cold,fully deionised water for 10 seconds. In the post-rinsing an addition offor example zirconium hexafluoride or of one of the organic substancesknown in principle may be employed, whereby a further improvement in thecorrosion resistance and paint adhesion of the coating may be achieved.

[0105] In the coating process according to the invention the metallicsurfaces can be prephosphated before the phosphating. The prephosphatingof substrates is advantageous if for example the prephosphated strip issubsequently formed/shaped or if parts are intermediately stored, bondedand/or welded in the corrosion-protected state. The substratespretreated in this way can thereby be much more easily formed/shaped andare protected against corrosion. In a particularly advantageous processvariant the metallic surfaces are welded, bonded and/or formed/shapedafter the phosphating (prephosphating) and are then optionallyrephosphated.

[0106] In most cases the phosphating plants in the automobile industryuse weakly alkaline cleaning agents, but in some cases also stronglyalkaline cleaning agents. It was surprising that the first crystallineprephosphating layer according to the invention is substantially moreresistant to the influence of strongly alkaline cleaning agents. Withthe short treatment times that are normally employed, the firstphosphate layer according to the invention was not or was only slightlyaffected by a strong alkaline cleaning agent.

[0107] The first and/or second phosphate layer applied to the metal partmay be wetted with an oil, a dispersion or a suspension, in particularwith a forming oil or anti-corrosion oil and/or with a lubricant such asa dry lubricant, for example with a wax-containing mixture. The oil orthe lubricant serves as additional temporary corrosion protection andmay in addition also facilitate a forming procedure, the unformed metalpart also having an increased corrosion resistance. A coating with anoil may also be of benefit for the second phosphate layer if the partsto be painted have to be transported to a distant paint shop.

[0108] Any oil layer or lubricant layer that is present can be removedfrom the first or second phosphate layer in order to prepare the coatingfor painting, forming, assembly, bonding or welding. The oil must beremoved before a subsequent paint coat, though it does not necessarilyhave to be removed for other process procedures.

[0109] The metal parts provided with a first and/or second phosphatelayer may be painted, coated with another type of organic coating and/orwith an adhesive layer, and then optionally formed/shaped, wherein themetal parts coated in this way may in addition be bonded and/or weldedto other parts. At the present time a very wide range of organiccoatings are known that can be used on a phosphate layer. In thisconnection not all organic coatings are covered by the definition ofpaints. The metal parts provided with a first and/or second phosphatelayer may be provided with a coating either before or only after theforming and/or assembly.

[0110] The phosphate-coated metal parts according to the invention mayif necessary be oiled in a so-called strip plant or may if necessary bedegreased and/or cleaned, before they are subsequently coated in a paintshop.

[0111] The phosphate-coated metal parts according to the invention mayif necessary be oiled for the production of for example equipmentlinings, may if necessary be formed/shaped and may if necessary may bedegreased and/or cleaned, before they are subsequently—if desired—coatedin a paint shop. For economic reasons the deoiling is preferably omittedbefore the bonding or welding.

[0112] The phosphate-coated metal parts according to the invention maybe oiled and formed/shaped for the production of for exampleautomobiles, in which connection several metal parts are then weldedtogether, bonded together or joined together in some other way,following which the assembled parts can be degreased and/or cleanedbefore they can subsequently be coated in a paint shop.

[0113] The metal parts coated by the process according to the inventionmay, as prephosphated metal parts, for a renewed conversion treatment orfor a renewed conversion pretreatment, in particular before beingpainted, or, as pretreated metal parts—in particular for the automobileindustry—especially before being painted or as end-phosphated metalparts that are optionally also subsequently painted, organically coatedin some other way and/or coated with a film, be coated with an adhesivelayer, formed/shaped, assembled and/or welded together. However, anormal precondition for welding is that the phosphate layer is not toothick and that any organic coating that optionally is applied iselectrically conducting.

[0114] In the coating process according to the invention the metal partsprovided with a first and/or second phosphate layer may be coated with apaint, with another type of organic coating, with a film and/or with anadhesive layer and if necessary formed/shaped, wherein the metal partscoated in this way may in addition be bonded or welded to other partsand/or may be joined to one another in a some other way.

[0115] Also a mix of various materials such as for example metal partsformed from uncoated steel and prephosphated metal parts can be coatednext to one another at the same time by a process according to theinvention without any problem.

[0116] In the case of pre-assembled or assembled metal parts a bettercorrosion protection than according to the aforementioned prior art canbe achieved in hollow spaces and cavities by the prephosphating, evenwithout application of a paint coat.

[0117] It may be advantageous to apply a passivating solution directlyto the first and/or second phosphate layer, in particular by spraying,dipping or rolling. In this case a post-rinse solution is preferablyused to further enhance the corrosion resistance and the paint adhesion,which solution may contain at least one substance based on Cr, Ti, Zr,Ce and/or other rare earth elements including lanthanum or yttrium,tannin, silane/siloxane, phosphorus-containing self-assemblingmolecules, phosphonates or polymers.

[0118] On comparing various types of metallic surfaces, such as forexample those of cold-rolled steel (CRS) and galvanised steels, the samephosphating solution produces significantly different results in somecases. With hot-dip galvanised steels (HDG) and with electrolyticallygalvanised steels (EG) the zinc that can dissolve out from thegalvanising has a marked effect on the bath composition. With HDG steelsthe content of aluminium in the HDG surface in certain circumstances hasa negative effect: in order to optimise the phosphating in the case ofHDG steels and aluminium surfaces an addition of fluorides in freeand/or bound form, for example as hydrofluoric acid or siliconhexafluoride, is then favourable.

[0119] Surprisingly the coating according to the invention is equivalentas regards corrosion resistance and paint adhesion to a comparable highnickel content coating, but is significantly cheaper and significantlymore environmentally friendly than the high nickel content coating. Inthis connection it is especially surprising that the high-grade coatingquality is largely independent of the chosen accelerator or acceleratormixture. The coating process according to the invention is alsounexpectedly robust. Furthermore, it was extremely surprising that thesame high-grade properties could be achieved by a Zn:Mn ratio in thevery wide range from 0.9:1 to 0.3:1. Moreover, the same high-gradeproperties could be obtained also outside this range provided thecomposition of the bath was suitably adapted.

[0120] The process according to the invention has the advantage comparedto the aforedescribed and implemented processes that it providesexcellent coatings with low consumptions of chemicals and comparativelylow costs, in particular of HDG, and is in this connection particularlyenvironmentally friendly. On account of the fact that no nickel is addedin this process, fewer heavy metals are discharged into the waste water,phosphate slurry and in the grinding dust. In contrast to similar baths,it is possible to reduce the bath temperature still further during thephosphating. On account of a slightly raised copper content the paintadhesion can be improved still further.

[0121] A concentrate for making up the phosphating solution or areplenishment solution for replenishing the phosphating solution maycontain in particular zinc, manganese, copper and phosphoric acid, butonly in certain cases alkalis and/or accelerators.

[0122] The substrates coated by the process according to the inventionmay be used for strip production, for the production of components orcar body parts or preassembled elements in the automobile or aerospaceindustry, in the building and construction industry, in the furnitureindustry, for the production of instruments and units, in particulardomestic appliances, measuring instruments, control devices, testingdevices, structural components, claddings/linings as well as smallparts; as wire, wire coiling, wire mesh, metal sheeting,cladding/lining, screening, car bodies or parts of car bodies, parts ofvehicles, trailers, mobile homes or missiles, as electronic ormicroelectronic components, as coverings, housings, lamps, lights,hanging light units, items of furniture or furniture parts, componentsof domestic appliances, frames, profiled sections, moulded parts ofcomplicated geometry, beam-barrier, radiator or sauna parts, automobilebumpers, parts of or with at least one pipe and/or a profiled section,window, door or bicycle frames, or as small parts such as for examplescrews, nuts, flanges, springs or spectacle frames.

EXAMPLES

[0123] The subject matter of the invention is illustrated in more detailwith the aid of embodiments:

[0124] The examples were carried out using the substrates and processsteps itemised hereinafter:

[0125] The test sheets consisted of an aluminium alloy AlMgSi ofthickness 1.2 mm or of uncoated, continuously annealed car body steel(CRS) or of steel galvanised on both sides with a coating of a hot-dipgalvanising (HDG) or of an electrolytic galvanising (EG) with a totalthickness of 0.7 mm. The surface area of the substrates was 400 cm²(measured over both surfaces).

[0126] a) The substrate surfaces were cleaned and thereby thoroughlydegreased in a 2% solution of an alkaline cleaning agent for 5 minutesat 60° C.

[0127] b) This was followed by rinsing with tap water for 0.5 minute atroom temperature.

[0128] c) The surfaces were then activated by dipping in atitanium-containing activation solution for 0.5 minute at roomtemperature.

[0129] d) The surfaces were then phosphated for 3 minutes at 55° C. bydipping in the phosphating solution.

[0130] e) The surfaces were next rinsed, first of all with tap water andthen with fully deionised water.

[0131] f) The coated substrates were then dried in a drying oven at 80°C. for 10 minutes.

[0132] g) Finally the dry test sheets were provided with a coat of acathodic dipping paint and coated with the further layers of a paintstructure conventionally used in the automobile industry for car bodyparts (layer structure and paints corresponding to Daimler Chrysler in“Moon Silver”)

[0133] The composition of the relevant phosphating solution as well asthe results of the tests are shown in Tables 1 to 3. TABLE 1 Compositionof the phosphating solutions in g/l or points of free acid (FA) or totalacid (TA) HA Zn Mn Ni Cu TiF6 + ZrF6** PO₄ NO₂ NO₃ etc. FA TA B 1 1.21.25 — 0.008 — 16.5 0.1 — — 1.8 32 B 2 1.2 1.5 — 0.008 — 18 0.1 3 — 1.832 B 3 1.2 2.5 — 0.008 — 18 0.1 3 — 1.8 32 B 4 1.4 2.5 — 0.010 — 16.5 —3 0.04 1.8 32 H₂O₂ B 5 1.4 1.5 — 0.015 — 16.5 — 5 1.5 HA 1.8 32 B 6 1.42.5 — 0.015 — 16.5 — 5 1.5 HA 1.8 32 B 7 1.4 1.5 — 0.025 — 16.5 — 5 1.5HA 1.8 32 B 8 1.4 2.5 — 0.025 — 16.5 — 5 1.5 HA 1.8 32 B 9 1.4 1.5 —0.040 — 16.5 — 5 1.5 HA 1.8 32 B 10 1.4 2.5 — 0.040 — 16.5 — 5 1.5 HA1.8 32 B 11 1.2 1.8 — — 0.003 + 0.002 18 — 3 1.5 HA 1.8 32 B 12 1.2 1.8— — 0.006 + 0.005 18 — 3 1.5 HA 1.8 32 B 13 1.2 1.8 — — 0.056 + 0.045 18— 3 1.5 HA 1.8 32 B 14 1.2 1.8 — — 0.011 + 0.008 18 — 3 1.5 H A 1.8 32 B15 1.2 1.8 — 0.008 0.003 + 0.002 18 — 3 1.5 HA 1.8 32 B 16⁺ 1.2 1.95 —0.008 0.003 18.8 — — 1.1 HA 3.4 32 (Ti) B 17⁺ 1.2 1.95 — 0.008 0.00418.8 — — 1.1 HA 3.4 32 (Zr) B 18 1.4 3.5 — 0.015 — 16.5 — 5 1.5 HA 1.832 B 19 1.2 1.3 — — 0.006 + 0.005 18 — 3 1.5 HA 1.8 32 B 20 1.2 2.5 — —0.006 + 0.005 18 — 3 1.5 HA 1.8 32 VB 1 1.2 0.5 — 0.005 — 18 0.1 3 — 1.832 VB 2 1.2 0.5 — 0.005 — 16.5 0.1 3 — 1.8 32 VB 3 1.2 0.8 — 0.005 — 180.1 3 — 1.8 32 VB 4 1.2 1.0 1.0 — — 18 0.1 3 — 1.8 32 VB 5 2.5 2.0 —0.008 — 18 — 3 1.5 HA 1.8 32 VB 6 1.2 1.0 — — — 18 0.1 3 — 1.8 32 VB 71.4 2.5 — 0.002 — 18 0.1 3 — 1.8 32 VB 8⁺ 1.2 1.95 — 0.005 — 18.8 — —1.1 HA 3.4 32

[0134] In addition the baths contained aminor amount to a certain amountof sodium as well as, for the pretreatment of aluminium surfaces, anamount of free fluoride in the range from 80 to 250 mg/l by addition ofammonium bifluoride. The total acid is given approximately. TABLE 2Results of the adhesion and corrosion tests on aluminium, steel orgalvanised surfaces, on coatings produced according to the invention (B)or in comparison examples (VB), obtained by 1. cross-hatch adhesion testaccording to DIN/EN ISO 2409 after storage for 40 hours in 5% NaClsolution (BMW specification), 2. stone impact test over 12 cyclesaccording to VW specification, and 3. salt spray/condensation wateralternating test over 12 cycles according to VDA 621-415. A = ground, B= unground. cross-hatch adhesion test Stone Impact Alternating TestScore Test acc. to VW acc. to VDA 621-415 Al % Paint Loss mm Creep CRSEG HDG A/B CRS EG HDG CRS EG HDG Al B 1 1 1 1 1.1 — — — — — — — B 2 1 11 1.1 — — — — — — — B 3 1 1 1 1.1 — — — — — — — B 4 1 1 1 1.1  2  5  80.5 2.0 1.8 — B 5 1 1 2.5 1.1  3 10  10 0.5 2.5 2.0 — B 6 1 1 1 1.1  3 6  12 0.5 2.0 1.5 — B 7 1 1 2 1.1  5 10  15 0.5 2.0 1.7 — B 8 1 1 0 1.1 4  5  6 0.5 2.0 1.5 — B 9 1 1 1.5 1.1  5  8  10 0.5 2.5 2.0 — B 10 0 00 1.1  3  4  5 0.5 2.0 1.3 — B 11 1 1 1 1.1 — — — — — — — B 12 1 0 1 1.1— — — — — — — B 13 0 0 1 2.1 — — — — — — — B 14 0 1 1 1.1 — — — — — — —B 15 1 1 1 1.0 — — — — — — — B 16 — — 0.5 — — — — — — — — B 17 — — 2.5 —— — — — — — — B 18 1 1 0 1.1  4  5  6 0.5 2.0 1.5 — B 19 1 1 2 1.1 — — —— — — — B 20 1 0 0 1.1 — — — — — — — VB 1 1 4 3 1.1  4 80 100 0.5 2.53.0 — VB 2 1 4 4 —  8 60  35 1.5 2.0 2.5 — VB 3 1 3 4 1.1  3 80  25 0.52.5 2.4 — VB 4 1 1 1 1.1  3  4  8 0.5 2.0 1.2 — VB 5 1 3 4 1.1 10 80  502.0 3.5 4.0 — VB 6 1 3 5 2.1 10 70  90 2.2 3.5 3.5 — VB 7 1 2 2 1.1  4 8  18 1.0 2.5 2.0 — VB 8 — 3.8 — — — — — — — —

[0135] In the cross-hatch adhesion test the scores ranged from 0 to 5for the best and for the worst results respectively. In the stone impacttest the percentage paint loss through the layer structure down to themetallic substrate surface is given in area %, while for the saltspray/condensation water alternating test the corrosive creep of thepaint starting from a scratch is given in mm. In all tests the resultsare mean values over in each case several tested sheets.

[0136] In the tests it was found that for all the results given in Table2, the results of the examples according to the invention were betterwith an increasing copper content or with a lower Zn:Mn ratio of thecopper-containing examples. The same is also true for an increasinghexafluoride content in titanium/zirconium/hafnium and for a reducedZn:Mn ratio of the copper-free examples. The combination of the coppercontent with the hexafluoride content in titanium/zirconium/hafniumindicates, at least for the content of titanium hexafluoride, asignificantly better improvement in the paint adhesion results, whichwere tested on the basis of the metal surface (HDG) that behaved mostbadly. The results vary only slightly however, depending on the type ofmetal surfaces. TABLE 3 Results of the corrosion tests on coatingsobtained according to the invention (B) and obtained in the comparisonexamples (VB) on the aluminium alloy AlMgSi and on thoroughly annealedsteel (CRS) by 1. Filiform test according to DIN EN 3665, 2. saltspray/condensation water alternating test over 12 cycles according toVDA 621-415, and 3. salt spray test according to DIN 50021 for steel,the following letters identifying the processing state: A = ground, B =unground Salt Spray/ Humidity Cycle Salt Spray Filiform Test Test Testmm Creep mm Creep mm Creep AlMgSi CRS A B A B B B 1 3.8 3.5 2.5 1.5 <1 B2 5.0 3.1 1.8 1.2 <1 B 3 5.3 1.3 1.8 0.3 <1 B 5 6.5 3.0 3.5  0.75 <1 B 66.0 4.0 4.0 0.5 <1 B 7 6.5 3.0 3.5 1.0 <1 B 8 5.7 1.3  1.75 0.5 <1 VB 14.5 43.3  2.2 1.5 <1 VB 2 — — — — 1.5 VB 3 6.1 5.2 3.3 1.0 <1 VB 4 4.02.5 2.0 1.0 <1

[0137] In the filiform test the mean value of the size of the filiformcorrosion phenomena in mm was measured. In the salt spray/condensationwater alternating test and in the salt spray test according to DIN 50021on steel the corrosive creep of the paint starting from a scratch wasgiven in mm on base metal. In all tests the results are mean values overin each case several tested sheets.

[0138] Since individual sites of such sheets are still always regroundin industrial coating, i.e. individual ground parts occur between thelargely unground surfaces, this comparison is significant for practicalpurposes.

[0139] In this connection it was found that when the aluminium alloy wastested by the filiform test, the expected reliability was not obtained,whereas in the salt spray/condensation water alternating test in somecases even better results were obtained in the samples coated accordingto the invention than in the nickel-containing phosphating.

[0140] Overall, the quality of the high nickel content phosphatings wasobtained with the tests of Table 2 and Table 3.

[0141] It was also found that the layer weight of the HDG sheets coatedaccording to the invention was almost constant, in the range from 2.0 to2.1 g/cm² with a manganese content in the range from 1 to 2.5 g/l, andwas almost exactly 1.0 g/cm² with a copper content in the range from 5to 20 mg/l.

[0142] In the prephosphating on the one hand compositions with a nitrateacceleration (B 21-B 23) and on the other hand with a nitrate-freeperoxide acceleration (B 24-B 26) were successfully tested and comparedto a nickel-free prephosphating and to a very low copper content or highnickel content phosphating (VB 26 and VB 27). Also, copper-free andrelatively high copper content phosphating solutions (VB 21-VB 24) wereused compared to the phosphating solutions according to the inventionwith a certain copper content. Hydrofluoric acid was added in fivetests. The sample sheets were treated, as in the experiments involvingExamples B 1 to B20, according to the steps a) to c), though thetitanium-containing activator was sprayed on. Layer weights in the rangefrom 1.5 to 1.6 g/m² were obtained. TABLE 4 Composition of theprephosphating solutions in g/l and points of free acid (FA) and totalacid according to Fischer (TAF) Zn Mn Ni Cu F_(total) PO₄ NH₄ NO₃* H₂O₂FA TAF B 21 1.74 2.15 — 0.010 — 20 — 15.5 — 2.6 19.2 B 22 1.74 2.15 —0.020 — 20 — 15.5 — 2.6 19.2 B 23 1.74 2.15 — 0.040 — 20 — 15.5 — 2.619.2 B 24 1.74 2.15 — 0.010 0.9 20 — — 1.0 3.4 19.2 B 25 1.74 2.15 —0.020 0.9 20 — — 1.0 3.4 19.2 B 26 1.74 2.15 — 0.040 0.9 20 — — 1.0 3.419.2 VB 21 1.74 2.15 — — — 20 — 15.5 — 2.6 19.2 VB 22 1.74 2.15 — 0.060— 20 — 15.5 — 2.6 19.2 VB 23 1.74 2.15 — — 0.9 20 — — 1.0 3.4 19.2 VB 241.74 2.15 — 0.060 0.9 20 — — 1.0 3.4 19.2 VB 25 1.70 2.0 1.3 — — 18.0 —12.0 — 2.9 19.0 VB 26 1.95 0.8 — 0.003 3.0** 18.5 0.9  3.2 1.2^(#) 3.019.4 VB 27 0.7 1.0 1.0 — — 17.5 —  2.1 — 0.8 18.0

[0143] In the comparison example 25 a nickel-containing prephosphatingwas applied in a layer weight of about 1.5 g/m², whereas in thecomparison examples 26 and 27 phosphate layers were applied in a layerweight of about 3 g/m². The comparison examples, like theprephosphatings according to the invention of the examples B 21 to B 26according to the invention (without post-phosphating), were painted witha automobile paint structure according to BMW and tested. In additionthe baths contained a very small to a specific amount of sodium. Due tothe high nitrate levels a comparatively minor amount of nitrite wasformed, which had a strongly accelerating effect. TABLE 5 Results of thecorrosion tests on electrolytically galvanised steel surfaces, oncoatings obtained according to the invention (B) and coatings obtainedin the comparison examples (VB) by 1. paint adhesion test by cross-hatchadhesion test method according to BMW test N 600 87.0 after 40 hours'storage in 5% NaCl solution at 40° C., 2. paint adhesion test bycross-hatch adhesion test/ condensation water test according to DIN/ENISO 2409 after 240 hours' storage in condensation water, 3. corrosionalternating test according to General Motors GM-SCAB Test 95-11 over 40cycles, and 4. corrosion test by weathering in the open air with NaClacceleration according to VDA 621-414. cross-hatch adhesion test- cross-condensation Open Air hatch water Test Weathering adhesion acc. to Testacc. test acc. DIN EN ISO GM-SCAB Test to VDA to BMW 2409 95-11 621-414Score Score mm Creep mm Creep B 21 3.0 2.0 1 0.3 B 22 1.0 1.0 1 0.3 B 231.0 1.0 1 0.3 B 24 — 2.5 1.5 — B 25 — 2.0 1 — B 26 — 2.0 1 — VB 21 5.05.0 3 0.8 VB 22 4.5 4.0 2 0.6 VB 23 — 4.5 2 — VB 24 — 4.0 2 — VB 25 2.01.5 1 0.3 VB 26 2.0 — 1 0.3 VB 27 1.5 1.0 1 0.3

[0144] Whereas in the two cross-hatch adhesion test scores of 0 to 5 canbe awarded, 0 being the best, in the corrosion tests the corrosivecreepage of the paint starting from a crack is specified in mm on basemetal. In all tests the results are mean values over in each caseseveral tested sheets.

[0145] In these tests it was found that the sheets coated according tothe invention have approximately the same quality as sheets with highnickel content phosphate coatings.

1. Process for the coating of metallic surfaces by manganese-zincphosphating with an aqueous phosphating solution, in which no nickel isintentionally added to the phosphating solution, characterised in thatthe zinc:manganese weight ratio of the phosphating solution ismaintained.in the range from 0.05:1 to 0.99:1, and that the phosphatingsolution has the following contents: zinc in the range from 0.05 to 5g/l, manganese in the range from 0.075 to 5.2 g/l, as well as copper inthe range from 0.008 to 0.050 g/l, and/or a total amount of 0.002 to 0.5g/l of hexafluoride complexes of boron, aluminium, titanium, hafniumand/or zirconium, calculated as F₆.
 2. Coating process according toclaim 1, characterised in that the phosphating solution has a content ofsilver in the range from 0.0001 to 0.05 g/l.
 3. Coating processaccording to one of the preceding claims, characterised in that thephosphating solution has a content of sodium in the range from 0.01 to10 g/l and/or a content of potassium in the range from 0.01 to 10 g/l.4. Coating process according to one of the preceding claims,characterised in that the zinc:phosphate weight ratio of the phosphatingsolution is maintained in the range from 0.016:1 to 1.33:1, phosphatebeing calculated as PO₄.
 5. Coating process according to one of thepreceding claims, characterised in that the phosphating solution has acontent of phosphate in the range from 3 to 75 g/l, phosphate beingcalculated as PO₄.
 6. Coating process according to one of the precedingclaims, characterised in that the phosphating solution has a chloridecontent in the range from 0.01 to 6 g/l and/or a chlorate content in therange from 0.01 to 5 g/l.
 7. Coating process according to one of thepreceding claims, characterised in that the phosphating solution has acontent of silicon hexafluoride in the range from 0.1 to 5 g/l. 8.Coating process according to one of the preceding claims, characterisedin that the phosphating solution has a content of free fluoride in therange from 0.001 to 0.8 g/l.
 9. Coating process according to one of thepreceding claims, characterised in that the phosphating solution has atotal content of fluoride in the range from 0.01 to 5 g/l.
 10. Coatingprocess according to one of the preceding claims, characterised in thatthe phosphating solution has a content of at least one accelerator inthe range from 0 to 40 g/l.
 11. Coating process according to one of thepreceding claims, characterised in that the phosphating solution has acontent of nitrite in the range from 0.01 to 0.3 g/l, a content ofnitrate in the range from 1 to 30 g/l, a content of compounds based onperoxide in the range from 0.001 to 3 g/l calculated as H₂O₂, a totalcontent of nitrobenzenesulfonate (NBS), nitropropane, nitroethane and/orother nitro-organic compounds—with the exception of compounds based onnitroguanidine—with oxidising properties in the range from 0.1 to 3 g/lcalculated as NO₂, a content of compounds based on nitroguanidine in therange from 0.1 to 5 g/l, a chlorate content in the range from 0.05 to 4g/l, a content of reducing sugar compounds in the range from 0.1 to 10g/l and/or a content of compounds based on hydroxylamine (HA) in therange from 0.1 to 6 g/l, calculated as HA.
 12. Coating process accordingto one of the preceding claims, characterised in that the phosphatingsolution has the following contents, in particular for parts: zinc inthe range from 0.6 to 1.4 g/l, manganese in the range from 0.7 to 2.0g/l, zinc:manganese weight ratio in the range from 0.6:1 to 0.95:1,phosphate calculated as PO₄ in the range from 12 to 25 g/l,zinc:phosphate weight ratio in the range from 0.02 to 0.12, copper inthe range from 0.008 to 0.025 g/l, total content of fluoride as freefluoride, as bound fluoride and/or as at least one complex fluoride, inthe range from 0 to 6 g/l, calculated as F, wherein the complex fluorideSiF₆ is contained in an amount in the range from 0 to 4.5 g/l calculatedas SiF₆, and nitrate in the range from 0 to 22 g/l and/or at least oneother accelerator selected from the group comprising nitrite orcompounds based on hydroxylamine, nitroguanidine and/or peroxide, ineach case in the range from 0.01 to 2 g/l.
 13. Coating process accordingto one of the preceding claims, characterised in that the phosphatingsolution has the following contents in particular for strip material,particularly preferably for galvanised strip surfaces: zinc in the rangefrom 0.1 to 4 g/l, manganese in the range from 0.5 to 5 g/l,zinc:manganese weight ratio in the range from 0.02:1 to 0.9:1, phosphatecalculated as PO₄ in the range from 10 to 40 g/l, zinc:phosphate weightratio in the range from 0.0025 to 0.4, copper in the range from 0.008 to0.032 g/l, total content of fluoride as free fluoride, as bound fluorideand/or as at least one complex fluoride in the range from 0 to 6 g/lcalculated as F, wherein the complex fluoride SiF₆ is contained in anamount in the range from 0 to 4.5 g/l, calculated as SiF₆, and nitratein the range from 0 to 22 g/l and/or at least one further acceleratorselected from the group comprising nitrite or compounds based onhydroxylamine, nitroguanidine and/or peroxide, in each case in the rangefrom 0.01 to 2 g/l.
 14. Coating process according to one of thepreceding claims, characterised in that the phosphating solution for theprephosphating has the following contents: zinc in the range from 1.3 to2.3 g/l, manganese in the range from 1.7 to 2.6 g/l, zinc:manganeseweight ratio in the range from 0.5:1 to 0.95:1, phosphate calculated asPO₄ in the range from 10 to 20 g/l, zinc:phosphate weight ratio in therange from 0.06 to 0.23, copper in the range from 0.008 to 0.048 g/l,total content of fluoride as free fluoride, as bound fluoride and/or asat least one complex fluoride in the range from 0 to 6 g/l calculated asF, wherein the complex fluoride SiF₆ is contained in an amount in therange from 0 to 4.5 g/l, calculated as SiF₆, and nitrate in the rangefrom 0 to 22 g/l and/or at least one further accelerator selected fromthe group comprising nitrite or compounds based on hydroxylamine and/ornitroguanidine, in each case in the range from 0.01 to 2 g/l, orperoxide in the range from 0.01 to 3 g/l.
 15. Coating process accordingto one of the preceding claims, characterised in that the phosphatingsolution has the following contents: zinc in the range from 0.6 to 1.4g/l, manganese in the range from 0.7 to 2.0 g/l, zinc:manganese weightratio in the range from 0.6:1 to 0.95:1, phosphate calculated as PO₄ inthe range from 12 to 25 g/l, zinc:phosphate weight ratio in the rangefrom 0.02 to 0.12, total content of fluoride as free fluoride, as boundfluoride and/or as at least one complex fluoride, in the range from0.012 to 6 g/l, calculated as F, wherein the total content of complexfluorides of titanium, hafnium and/or zirconium is in the range from0.002 to 0.5 g/l, calculated as F₆, and wherein the complex fluorideSiF₆ is contained in an amount in the range from 0 to 4.5 g/l,calculated as SiF₆, and nitrate in the range from 0 to 22 g l and/or atleast one further accelerator selected from the group comprising nitriteor compounds based on hydroxylamine, nitroguanidine and/or peroxide, ineach case in the range from 0.01 to 2 g/l.
 16. Coating process accordingto one of the preceding claims, characterised in that the metallicsubstrates are coated for a time of up to 20 minutes, wherein stripmaterial is preferably coated for a time of 0.1 to 120 seconds andparticularly preferably for a time of 0.3 to 60 seconds, and whereinparts are preferably coated for a time from 1 to 12 minutes andparticularly preferably for a time from 2 to 8 minutes.
 17. Coatingprocess according to one of the preceding claims, characterised in thatthe temperature of the phosphating solution in the coating procedure isin the range from 10° to 72° C., wherein strip material is preferablycoated in the range from 40° to 70° C. and wherein parts are preferablycoated in the range from 20° to 60° C. and particularly preferably inthe range from 32° to 58° C.
 18. Coating process according to one of thepreceding claims, characterised in that the free acid has a value of 0.1to 10 points, the total acid according to Fischer has a value of 5 to 50points, and the ratio of the total acid according to Fischer to freeacid is in the range from 0.01 to 0.7.
 19. Coating process according toone of the preceding claims, characterised in that the pH of thephosphating solution is in the range from 1 to
 4. 20. Coating processaccording to one of the preceding claims, characterised in that thephosphating solution is applied to the surface of the substrates byknife coating, flow coating, spraying, sprinkling, brushing, dipping,nebulising or rolling, wherein individual process steps may be combinedwith one another, the application optionally being followed by squeezingoff.
 21. Coating process according to one of the preceding claims,characterised in that substrates with a metallic surface predominantlycontaining aluminium, iron, copper, magnesium, tin or zinc are coatedwith the phosphating solution, in particular surfaces of at least one ofthe materials based on aluminium, iron, steel, zinc and/or alloys with acontent of aluminium, iron, copper, magnesium, tin or zinc.
 22. Coatingprocess according to one of the preceding claims, characterised in thata phosphate coating that has a layer weight in the range from 0.2 to 6g/m² is deposited from the phosphating solution.
 23. Coating processaccording to one of the preceding claims, characterised in that themetallic surfaces are cleaned, pickled, rinsed and/or activated beforethe phosphating.
 24. Coating process according to one of the precedingclaims, characterised in that the metallic surfaces are galvaniseddirectly before the phosphating.
 25. Coating process according to one ofthe preceding claims, characterised in that the metallic surfaces areprephosphated.
 26. Coating process according to claim 25, characterisedin that the phosphating solution for the prephosphating has thefollowing contents: zinc in the range from 0.4 to 5 g/l, manganese inthe range from 0.5 to 5.2 g/l, copper in the range from 0.008 to 0.050g/l.
 27. Coating process according to claim 25 or 26, characterised inthat at least partially prephosphated, optionally at least partiallyformed/shaped, optionally at least partially welded metallic substratesare phosphated by coating with an aqueous phosphating solution, in whichno nickel is intentionally added to the phosphating solution or thecoating is carried out only with a nickel content of the phosphatingsolution of up to 0.3 g/l, wherein the phosphating solution has thefollowing contents: zinc in the range from 0.05 to 5 g/l, and manganesein the range from 0.075 to 5.2 g/l.
 28. Coating process according to oneof the preceding claims, characterised in that the phosphated substratesare rinsed at least once and are optionally treated between two rinseprocedures with a post-rinse solution to provide additional passivation.29. Coating process according to one of the preceding claims,characterised in that after the phosphating the metallic surfaces arewelded, bonded and/or formed/shaped, and are then optionallyrephosphated.
 30. Coating process according to one of the precedingclaims, characterised in that the metal parts provided with a firstand/or second phosphate layer are coated with a paint, with another typeof organic coating, with a film and/or with an adhesive layer and areoptionally formed/shaped, wherein the metal parts coated in this way mayin addition be bonded or welded to other parts and/or joined together insome other way.
 31. Coating process according to one of claims 1 to 30,characterised in that the metal parts provided with a first and/orsecond applied phosphate layer are coated either before or after theforming and/or assembly with a coating corresponding to claim
 29. 32.Use of the metal parts coated by the process according to at least oneof claims 1 to 31 as prephosphated metal parts for a renewed conversiontreatment or for a renewed conversion pretreatment, in particular beforepainting, or as pretreated metal parts in particular for the automobileindustry, especially before painting, or an end-phosphated metal parts,which may optionally also subsequently be painted, organically coated inanother way and/or coated with a film, with an adhesive layer,formed/shaped, assembled and/or welded together.
 33. Use of thesubstrates coated by the process according to at least one of claims 1to 31 in the production of strip material, for the production ofcomponents or car body parts or preassembled elements in the automobileor aerospace industry, in the building and construction industry, in thefurniture industry, for the production of instruments and units, inparticular domestic appliances, measuring instruments, control devices,testing devices, structural components, claddings/linings as well assmall parts; as wire, wire coiling, wire mesh, metal sheeting,cladding/lining, screening, car bodies or parts of car bodies, parts ofvehicles, trailers, mobile homes or missiles, as electronic ormicroelectronic components, as coverings, housings, lamps, lights,hanging light units, items of furniture or furniture parts, componentsof domestic appliances, frames, profiled sections, moulded parts ofcomplicated geometry, beam barrier, radiator or sauna parts, automobilebumpers, parts of or with at least one pipe and/or a profiled section,window, door or bicycle frames, or as small parts such as for examplescrews, nuts, flanges, springs or spectacle frames.